A lithium-ion secondary battery is widely used as a secondary battery having a high capacity and a high voltage for a camera, a personal computer, an electric automobile or the like. The negative-electrode carbon material composing the negative-electrode of a lithium-ion secondary battery influences the performance of a lithium-ion secondary battery. As the negative-electrode carbon material for a lithium-ion secondary battery, a carbon-based negative-electrode carbon material or a graphite-based negative-electrode carbon material is known.
The carbon-based negative-electrode carbon material is classified into a hard carbon-based one and a soft carbon-based one. Pulverizing, classifying and carbonizing a phenolic resin, a naphthalene sulfonic acid resin, polyvinylidene chloride, carboxymethylcellulose, a polyacrylonitrile resin or the like result in the hard carbon-based negative-electrode material. Pulverizing, classifying and carbonizing polyvinyl chloride, a gilsonite coke, a petroleum or coal mesophase pitch and a petroleum coke or a coal pitch coke obtained by carbonizing the pitch at 300 to 500° C. (a calcination treatment) or the like result in the soft carbon-based negative-electrode material.
As the graphite-based negative-electrode carbon material, a negative-electrode carbon material for a lithium-ion secondary battery having a reduced surface area is known, in which the surface of graphite particles is vapor-deposited with a pyrolyzed carbon by a CVD method (Patent Literature 1). In addition, a carbon-based negative-electrode carbon material having a reduced surface area is also known, in which the surface of a carbon-based negative-electrode carbon material obtained as described above is vapor-deposited with a pyrolyzed carbon by a CVD method.
FIG. 5 is a block diagram illustrating an example of an apparatus for manufacturing a negative-electrode carbon material with the use of a conventional chemical vapor deposition furnace. In FIG. 5, the reference sign 900 represents a conventional apparatus for manufacturing a negative-electrode carbon material, and to a cylindrical chemical vapor deposition furnace 91, a graphite-particle supply opening 97 and a negative-electrode carbon material recovery opening 99 are formed. Within the chemical vapor deposition furnace 91, stirring blades 93 driven by a motor 95 are provided, which stir the interior of the chemical vapor deposition furnace 91. To the chemical vapor deposition furnace 91, a carbon vapor deposition source supply opening a for supplying a source for carbon vapor deposition, along with an inert gas, into the chemical vapor deposition furnace 91, an inert gas supply opening b for supplying an inert gas to the interior of the chemical vapor deposition furnace 91, and a gas exhaust opening c for exhausting a gas within the chemical vapor deposition furnace 91 to the exterior of the furnace 91 are provided. To the chemical vapor deposition furnace 91, a heater for heating the interior of the chemical vapor deposition furnace 91 is provided (not illustrated). The negative-electrode carbon material recovery opening 99 is connected via an on-off valve 101 to a container 103.
By using this apparatus for manufacturing a negative-electrode carbon material, a negative-electrode carbon material is manufactured as follows. First of all, to the interior of the chemical vapor deposition furnace 91, graphite particles are supplied. The graphite particles supplied to the interior of the chemical vapor deposition furnace 91 are heated by the non-illustrated heater, while being in a fluid condition within the chemical vapor deposition furnace 91 by the ascending current of an inert gas supplied through the inert gas supply opening b, and the stirring caused by the stirring blades 93. When the temperature within the chemical vapor deposition furnace 91 reaches 650 to 1200° C., a source for carbon vapor deposition is supplied through the carbon vapor deposition source supply opening a to the interior of the chemical vapor deposition furnace 91. The source for carbon vapor deposition supplied to the interior of the chemical vapor deposition furnace 91 comes into contact with the surface of the graphite particles, along with pyrolyzes, thereby being vapor-deposited onto the surface of the graphite particles. In this way, the graphite particles onto the surface of which the pyrolyzed carbon is vapor-deposited, in other words the negative-electrode carbon material, are obtained. The interior of the chemical vapor deposition furnace 91 is in a non-oxidizing atmosphere by an inert gas supplied through the inert gas supply opening b, in order to prevent rapid oxidation of the graphite particles or the negative-electrode carbon material. The negative-electrode carbon material formed within the chemical vapor deposition furnace 91 by the above described chemical vapor-depositing treatment is cooled under the non-oxidizing atmosphere within the chemical vapor deposition furnace 91, until the temperature reaches a temperature at which the negative-electrode carbon material is not oxidized even under an oxygen-containing atmosphere. Therefore, the temperature within the chemical vapor deposition furnace 91 after the negative-electrode carbon material is taken out from the chemical vapor deposition furnace 91 decreases to 500° C. or lower.
When a plurality of batches of negative-electrode carbon materials are manufactured by using this conventional apparatus 900 for manufacturing a negative-electrode carbon material, the temperature within the chemical vapor deposition furnace 91 in supplying graphite particles to the interior of the chemical vapor deposition furnace 91 lowers. Accordingly, the temperature within the furnace must be recovered (raised) to a temperature at which the chemical vapor-depositing treatment may be initiated. Note that, when carbon-based precursor particles are burned, a supply of the source for carbon vapor deposition through the carbon vapor deposition source supply opening a provided to the chemical vapor deposition furnace 91 is unnecessary, but only a supply of an inert gas supplied through the inert gas supply opening b is sufficient for the carbonizing treatment. From the above described burned carbon, the negative-electrode carbon material may be obtained onto which a pyrolyzed carbon has been chemically vapor-deposited with the use of the chemical vapor deposition furnace, like the graphite particles. Using the chemical vapor deposition furnace makes it also possible to carry out a carbonizing treatment and a chemical vapor-depositing treatment in parallel.
Because the above described cooling and temperature-raising steps are included, in a process for manufacturing a negative-electrode carbon material, the using time of the chemical vapor deposition furnace and the carbonizing furnace is long. Therefore, the productive efficiency is poor.